Field of the Invention
The invention relates to an integrated circuit having a self-test device for carrying out a self-test of the integrated circuit.
An integrated circuit of that type is described in U.S. Pat. No. 5,173,906, for example. The self-test device, a so-called built-in self-test system, is an integral part of the integrated circuit. It contains a test pattern generator for generating test signals which are fed to circuit units of the integrated circuit that are to be tested. Result signals concerning the test that has been carried out are generated On-Chip and are read out to a point outside the chip after the test has been carried out. The test signals are transmitted from the self-test device to the circuit units to be tested through data lines situated on the chip.
It is accordingly an object of the invention to provide an integrated circuit having a self-test device, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which affords improved testability through the use of its self-test device.
With the foregoing and other objects in view there is provided, in accordance with the invention, an integrated circuit, comprising a circuit unit to be tested, the circuit unit having an input; a contact-making point of the circuit for external contact-making, the contact-making point connected to the input of the circuit unit of the integrated circuit to be tested; and a self-test device for carrying out a self-test of the integrated circuit, the self-test device having an output connected to the contact-making point, and the self-test device feeding a test signal through the contact-making point to the circuit unit to be tested.
Therefore, in contrast to conventional circuits, the test signals are deliberately passed through the contact-making point which, by way of example, may serve for external contact-making through the use of test tips of a test unit or through the use of a bonding wire. The advantage which this procedure has over direct feeding of the test signal to the input of the circuit unit to be tested is that, in this way, the connection between the contact-making point and the input of the circuit unit to be tested is also tested. Consequently the test signal is fed to the circuit unit to be tested in a manner that is the same as the case when the test mode is not concerned, with signals fed in externally through the contact-making points. Therefore, in contrast to previous solutions, the invention makes it possible to test the connection between the contact-making point and the circuit unit to be tested without necessitating complicated changes to the integrated circuit or its self-test device. The output of the self-test device merely has to be connected to the contact-making point, instead of directly to the input of the circuit unit to be tested. In particular, the structure of the self-test device and the type of test patterns or test signals generated by that self-test device, as well as the way in which a result signal is generated for the test that has been performed and the outputting of the results to a point outside the integrated circuit, can be configured in exactly the same way as in conventional integrated circuits with self-test devices.
In accordance with another feature of the invention, the contact-making point is connected through an input driver to the input of the circuit unit to be tested, for feeding external signals to the circuit unit to be tested, in a normal operating mode of the integrated circuit; and the self-test device transmits the test signal to the contact-making point and from there through the input driver to the input of the circuit unit to be tested, in a test operating mode.
This has the advantage of resorting to components that are already required in the normal operating mode, namely the input driver data lines connected thereto, in order to feed the test signal to the circuit unit. Moreover, in this way this input driver is included in the testing by the self-test device.
In accordance with an additional or alternative feature of the invention, the output of the circuit unit is connected through an output driver to the contact-making point, for outputting signals of the circuit unit to a point outside the integrated circuit, in the normal operating mode; the output of the self-test device is connected through the output driver to the contact-making point; and the self-test device transmits the test signal through the output driver to the contact-making point, in the test operating mode.
This development affords the advantage of only requiring a single output driver in order to transmit the test signal from the self-test device to the contact-making point on one hand, in the test operating mode, and for outputting signals of the circuit unit through the contact-making point to a point outside the integrated circuit on the other hand, in the normal operating mode. Moreover, the output driver is included in the testing by the self-test device.
Both developments of the invention afford the advantage of permitting the test signal to be transmitted from the self-test device to the contact-making point, and from the contact-making point to the input of the circuit unit to be tested, through drivers that are already required in the normal operating mode and are therefore present in any case. As a result, no additional electrical connections and drivers need be provided. Furthermore, as a result of the test signal being fed through the two drivers, both the input driver of the circuit unit to be tested and its output driver are tested by the self-test device. Therefore, not only the circuit unit to be tested but also the drivers and the lines connected thereto are tested with little outlay.
In accordance with a concomitant feature of the invention, the output of the self-test device is connected to the output of the circuit unit in such a way that the self-test device transmits the test signal, in the test operating mode, first of all to the output of the circuit unit and from there through the output driver to the contact-making point.
This has the advantage of including the entire output data path of the circuit unit, from the output thereof as far as the contact-making point, in the testing by the self-test device.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an integrated circuit having a self-test device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.